function _(id){
		return document.getElementById(id);
}
var picture = document.getElementById('picture');
var scl = document.getElementById('scl');
var timer;
var num = 0;/*判断是否发到头*/
timer = setInterval(marquee,10);
function marquee(){   /*marquee不能做无缝滚动*/
    num--;
    if(num<-2200){
    	num = 0;
    }
   _('picture').style.left = num +'px';
}
    _('scl').onmouseover = function (){
      	clearInterval(timer);
}
    _('scl').onmouseout = function (){
       timer = setInterval(marquee,10);
}